Check valve for vacuum pump



March 19, 1963 CHECK VALVE FOR VACUUM PUMP Original Filed Dec. 2, 1958 3Sheets-Sheet 1 INVENTOR.

Keane-m F. wessuufi A-rws,

, March 19, 1963 K. F. WESSLING 3,

CHECK VALVE FOR VACUUM PUMP Original Filed Dec 2, 1958 2 3 I 9 g 1 I i g9 I I g 5 a 4 93 I z '4 6M v INVENTOR- KENNETH F: 55mm Marh 19, 963

K. F. WESSLING CHECK VALVE FOR VACUUM PUMP Original Filed Dec. 2, *19583 Sheets-Sheet 3 ATmsPHEmc INV ENT OR. Keuue'm FI Wassunfi BY Mafia WA'rws United States Patent tion of Illinois Original application Dec. 2,1958, Ser. No. 777,666, now Patent No. 3,040,793, dated June 26, 1962.Divided and this application Nov. 9, 1959, Ser. No. 851,647

4 Claims. (Cl. 230--229) The present invention relates generally tocheck valves for vacuum pumps and more particularly to a check valve fora vane type pump capable of pumping down to pressures on the order ofmicron or better. 'Such a vane type pump is disclosed in my copendingapplication Serial No. 777,666, now Patent No. 3,040,793, of which thepresent application is a division.

It is an object of the invention to provide va vacuum pump check valvewhich is highly efficient in operation and which runs quietly, free fromthe clatter characteristic of conventional pump valves. It is a moredetailed object to provide a novel check valve construction which iscapable of holding a high vacuum, which is required to cycle at a highrepetitive rate, and which has novel means for insuring prompt openingand cushioned closing.

It is an additional object of the invention to provide a valveconstruction which is positive and elficient in operation but which hasnovel provision for controlled reverse leakage of oil during part ofeach vacuum pumping cycle.

Other objects and advantages of the invention will become apparent uponreading the attached detailed description of the reference to thedrawings in which:

FIGURE 1 is an axial section taken vertically through a two stage vanetype vacuum pump in which the present invention is incorporated.

FIG. 2 is a transverse section taken along the line 2-2 in FIG. 1. FIG.2a is a section taken along the line 2a2a in FIG. 1.

FIG. 3 is an enlarged top view of the valve member and surrounding tray.

FIG. 4 is a section taken along the line 4-4 in FIG. 3.

FIG. 5 is a section taken along the line 55 in FIG. 2.

FIGS. 6a-6d are a series of stop motion views showing the operation ofthe check valve when pumping air prior to reaching rated vacuum.

FIG. 7 shows the variations of pressure at the outlet port of the pumpfor the steps of motion set forth in FIGS. 6a-6d.

While the invention has been described in connection with a preferredembodiment it will be understood that I do not intend to limit theinvention to such embodiment, but intend to cover the alternative andequivalent constructions which may be included within the spirit andscope of the appended claims.

Turning now to the drawings, the check valve is shown included in atwo-stage rotary vane type vacuum pump for which it has been found to bewell suited. However,

no attempt has been made to limit the invention to such a preferredconstruction, since such a valve mayalso be employed in other types ofvacuum pumps, In the pump shown it may be noted in FIGS. 1 and 2 thatthe housing includes an end member 15 which seats a cup-shaped enclosure16 having a flange secured by suitable screws 17. Mounted on the top ofthe end member 15 is an inlet port 20. For providingv access, the topsurface of the housing 16 is enclosed by an access plate 21 whichcarries a vent cap 22 thereon of flat disc shape.

As is usual in vacuum pumps, the inlet port 20 is connected to thesystem to be evacuated and, upon driving of the pump by a motor, the airor gas withdrawn from the system is discharged from under the vent cap.In

3,081,936 Patented Mar. 19, 1963 the following discussion it will beassumed that air is being pumped.

The internal construction of the pump is shown in the remainder of thefigures and particularly FIG. 1. EX- tending longitudinally through thepump is a shaft 30, one end of which is journaled in the end member 15and the other end of which is journaled in a bearing or end plate 31. Aseal indicated at 32 is interposed between the shaft and the enclosure16 to prevent escape of the sealing and lubricating oil.

Surrounding the shaft at its left hand end is a first stage or pumpingunit 40 having a stator 41 in the form of a ring made of cast iron orthe like having an irregular outline and a circular opening 42 which iseccentric with respect to the shaft 30. Mounted within the opening 42 isa rotor 43 in the form of a metal disc having accurately groundendfaces, the rotor being in contact with the stator at a terminalregion 4311. The rotor 43 is secured to the shaft by a key 44 and isslotted to accommodate radially extending vanes which are spring pressedoutwardly against the stator by means of coil spring 47, assembled on aradially extending pin 49.

For the purpose of admitting air from the inlet 20 into the spacebetween the rotor and stator it may be understood that an opening (notshown) is provided in the wall of the end member 15. Moreover, forconducting the air, the edges of the opening 42 are grooved or relievedto provide inlet ports 51, 52 which are interconnected by an axiallyextending passage 53 (FIG. 2). For discharge of air from the first stage40, outlet ports are formed in the stator of similar thickness andcontour and symmetrically located on the opposite side of the region ofcontact 43a between stator and rotor. These outlet ports are indicatedat 55, 56 and interconnected by a passage 57 (FIG. 2).

The second stage or pumping unit, indicated at 60 in FIGS. 1 and 2 issubstantially identical to the first. It includes a stator 61 having acentral opening 62 accommodating a rotor 63 which is in contact with thestator at the terminal region 63a. The rotor is keyed to the shaft 30 bya key 64. Slidably mounted in the rotor are vanes 65, 66 outwardlypressed byspring 67, on a guide pin 69. The second stage has inlet ports71, 72 formed on the inner surface of the stator and interconnected bya-passage 73, as well as outlet ports 75, 76 interconnected by a passage77.

Interposed between the two stages 40, 60 is a center plate 80 havingfiat, finely machined side surfaces which bear against the side surfacesof the rotors 43, 63. For providing communication between the outletport 56 of the first stage and the inlet port 71 of the second, it willbe understood that the center plate 80 has an appropriate passage ortransfer port (not shown). To keep the shaft 30 from moving endwiserelative to the center plate the shaft is provided with thrust washers83, 84 which are accommodated in annular recesses 85, 86 machined oneach side of the center plate as shown. For the purpose of supplyinglubricant between the stages and thereby to insure that the first stageis lubricated by oil leaking into the second stage, the center plate 80is provided with an opening 88 which interconnects the recesses 85, 86(FIG. 1). v I In accordance with the present invention, a novel checkvalve is provided at the outlet port 78 of the second stage, including aleaf spring which in its normal, unstressed state is spaced from the.land around theport 78 and which provides intentional leakage of oilinto the pump mechanism during a portion of each pump-ing cycle. Furtherin accordance with the invention I employ a composite leaf springconstruction including a lower leaf spring and an upper leaf springarranged flatly faceato-face with the lower leaf spring having anopening therein registered with the outlet port and the upper leafspring having a combined sealing and cushioning member for sealing theopening in the lower leaf spring to produce a novel and quiet sealingaction. Thus, referring to the drawings and particularly to FIGS. 3 and4, a check valve 100 is provided having a lower leaf spring 101 and anoverlying or upper leaf spring 102 arranged flatly adjacent thereto. Theleaf springs are mounted at their stationary ends by machine screw 103or the like. In carrying out the present invention the lower leaf spring101 is spaced, as shown, above the land 79 which surrounds the outletport 78 of the second pumping stage, spacing being provided by a spacer104 surrounding the mounting screw. Registering with the outlet port78a, and formed in the end of the spring 101 is a circular opening 105having a diameter which is substantially the same as that of the mouthof the port, which mouth may be desirably formed by chamfering asindicated at 78a. It will be apparent that because of the spacer 104 thelower spring 101, in its unstressed state, is spaced above the land 79by an amount indicated at 106.

Interposed between the leaf springs 101, 102 for sealing the opening 105in the first leaf spring is a sealing and cushioning disc 110 which ispreferably secured to the upper leaf spring 102 by a rivet 111 or thelike. A spacer 112 between the springs at their fixed ends separatesthem an amount which is substantially equal to the thickness of thesealing member 110.

With regard to the materials of construction of the check valvedescribed above, for use in a pump of the size shown, the leaf spring.101, 102 are preferably formed of flat clock spring stock having athickness of approximately 0.010 inch. The sealing member 110 which mayhave a thickness of 0.030 inch, is formed of plastic material,preferably a polytetrafiuoroethylene resin widely available under thename of Teflon, although other materials having approximately the samephysical characteristics may be employed. Preferably the material shouldhave a hardness within the range of D50 to D65 as measured by theA.S.T.M. method D676. The deformation under load should not exceed 4-8percent when subjected to a pressure of 1200 p.s.i. in a period oftwenty-four hours in accordance with A.S.T.M. method D621. The modulusof elasticity should preferably be on the order of 58,0000 p.s.i. inaccordance with A.S.T.M. method D638, the above figures being set forthfor the guidance of those wishing to employ substitute materials withoutdeparting from the present invention.

With regard to the leakage gap indicated at 106 in FIG. 4, myobservations show that using conventional lubricating and sealing oiland with the valve submerged to a shallow depth under an oil level 113this gap may be on the order of 0.060 inch in a pump of the size shownhere.

It is found that employing a valve constructed along the lines set fortha number of important and unexpected advantages are derived. Notably,the valve operates quietly free of the clatter which characterizesconventional pumps. It will be appreciated by one skilled in the artthat vacuum pumps employed in laboratories are frequently left connectedto an evacuating system for long periods of time and the clatter set upby one or more of the vacuum pumps in constant operation is bothersomeand distracting to those working in a laboratory. The present design ofpump, by contrast, produces only slightly more noise than the motorwhich drives it and a large number of pumps may be operatedsimultaneously in the same room without raising the noise level to anobjectionable degree.

Pumps equipped with the above valve construction are eificient and arefound to make maximum use of the sealing and lubricating oil, permittinghigh vacuums to be drawn and sustained over long periods of time withoutany detectable wear of the valve elements and without any change in theoperating characteristics. The high efliciency of the valve isparticularly surprising in view of the fact that it includes what may betermed a built-in leak. That is to say, when the leaf springs occupy thenormal, unstressed position illustrated in FIG. 4, the gap 106 providessufficient area for substantial leakage of oil into the port 78. Duringthe portion of the operating cycle when the pressure within the port 78is at or only slightly below atmospheric pressure, the vacuum is notsufiicient to overcome the spring force to effect closure of the valve.Consequently oil is sucked through the gap and down into the secondstage of the pump. The oil which is thus drawn in eficctively seals therotor to the stator so that there is no leakage or bypassing of air fromoutlet to inlet. During a subsequent portion of the pumping cycle, theoil which has been drawn in is forcibly expelled and the cycle isrepeated.

While the features and advantages of the check valve described abovehave been found to be important to the operation, the operativephenomena are the subject of continuing investigation. Nevertheless, forfurther understanding, reference may be made to a series of stop motionviews FIGS. 6a-6d which show the operation of the valve when pumping airand prior to the time that a complete vacuum is drawn. In FIG. 7, andarranged adjacent the stop motion figures, there is shown an approximateplot of pressure variations relative to atmospheric pressure which occurwithin the outlet port 78, keeping in mind that the purpose of FIG. 7 isto show the direction of pressure variation during the cycle rather thanto indicate the magnitude of the variation.

Thus referring to FIG. 6a it will be assumed that the pressure in theport 73 has just gone through atmospheric and is slightly belowatmospheric. The force is, however, not suificient to draw the leafsprings downwardly into contact with the land surrounding the port.Consequently oil is drawn in through the gap 106 into the port and intocontact with the rotor. As the vacuum in the port 78 increases, both thesprings 101, 102 are drawn down tight into contact with the land 79 sothat no further oil can enter. As the cycle continues, the active vanein the rotor 63 causes the air between rotor and stator to be compressedso that the pressure in the outlet port 78 rises above atmosphericpressure as shown in FIG. 6c. This causes unse'ating of the leaf springsfrom the land. Experience shows that the metallic surface on theunderside of the spring 101 is separated from the metallic surface ofthe land 79 with ease. However, the plastic-to-metal seal between thesealing member and the upper surface of the leaf spring 101 is not quiteso readily broken, so that the leaf spring 101 remains in contact withthe sealing member during the initial portion of its upward movement.Since the lower spring tends to resist moving upwardly by reason of itsresilience, a point in the movement will be reached where the upperspring separates from the lower as shown in FIG. 6d, whereupon the lowerspring is free to assume its initial at rest condition shown in FIG. 6a.The upper spring, however, remains distorted upwardly until the blow offis complete following which it, too, will be restored to the initialposition shown in FIG. 6a in readiness for the ensuing cycle ofoperation. During the time that the valve is in operation, air bubbleswill be seen escaping from under the tips of the springs 101, 102, withthe bubbles becoming smaller in size as a high vacuum is drawn.Indicative of proper operation of the valve it is noted in operationthat the surface of the oil becomes humped as indicated by the dottedoutline 116 in FIGS. 4 and 6a. Such humps indicate that oil is beingpumped back and forth by reason of vibration of the leaf springs.

As the vacuum increases, the excursion of the leaf springs will beaccordingly reduced, but even under conditions of full rated vacuum thesprings continue to vibrate, in a practical pump, through a distance onthe order of a 3 inch and observation shows that under such high vacuumconditions oil continues to be pumped in and out of the pump through theport 78 during each cycle of operation.

Further in accordance with the present invention, the check valve isaccommodated in a shallow well or recess formed in the upper surface ofthe stator 61 thereby to limit the total amount of oil which may bedrawn reversely through the pump. In the present instance this functionis taken care of by providing a surrounding dam or tray 1120 having amounting portion 121 and a sidewall 122. In order to provide clearanceabout the leaf springs 101, 102, the mounting portion 121 is formed witha rectangular opening 123 as shown in FIG. 3. Arranged under the tray120 is a gasket 124, the thickness of metal and gasket serving to spacethe lower spring from the orifice by the 0.060 inch previouslymentioned. Thus at one end the tray is held by the mounting screw 103;at the other end a screw 125 is provided.

During normal operation of the pump the oil level 113 is preferably suchas to cover the check valve 1% reliably, say to a depth on the order ofto inch. However use of the tray 120 insures that the check valve iskept under a reliable depth of oil while nevertheless severely limitingthe amount of oil which may be sucked reversely back into the system. Asillustrated in FIG. 4, the limited amount of oil which can be suckedback to the system in the present construction is indicated by the crosshatched area 126, the line of the oil being at or only slightly abovethe upper edge of the tray 120. Thus, as soon as sufficient oil haspassed through the port '78 to drop the oil level to the upper edge ofthe tray, no further oil can flow into the tray and the bulk of-the oilis prevented from being sucked back into the pump. This insures that thereversely sucked oil will be accommodated by the space 115 in the endmember 15 even though such space is of relatively limited volume. If thetray were not utilized, sufficient available oil would completely fillall recesses of the exhaust stage thus preventing a motor-powered start.Thus in the present construction, in spite of the use of a valve havingan intentional gap" through which oil can flow on shutdown, the oil isprevented from blocking rotation when the pump is again operated. Thepresent valving arrangement therefore not only insures high efiiciencyduring operation but high reliability in start I up.

I claim as my invention:

1. In a vacuum pump a combination comprising a frame, a pump unit insaid frame having an inlet port and an exhaust port surrounded by a landportion, a check valve covering said exhaust port, said check valveincluding an upper leaf spring and a lower leaf spring arranged flatlyface-to-face, said lower leaf spring being slightly spaced away from theland surrounding said port when the leaf springs are in their unstressedcondition, and said lower spring having an opening therein centered withrespect to said exhaust port, a cushioning and sealing member interposedbetween said springs for sealing the opening in the lower spring when avacuum is drawn in the inlet port, and means providing an oil bath forsubmerging said springs at a shallow depth under oil during theoperation thereof.

2. In a vacuum pump a combination comprising a frame, a pump unit insaid frame having an inlet port and an exhaust port, a check valvecovering said exhaust port,

said check valve including a fiat leaf spring secured at on end andcovering said exhaust port, means providing an oil bath for submergingsaid spring at a shallow depth under oil during the operation thereof,said leaf spring being slightly spaced away from said exhaust port whenthe leaf spring is in its unstressed condition so that oil is suckedreversely through said check valve during a portion of each pumpingcycle of the pump unit, and means surrounding said spring for dammingand thereby limiting the flow of oil drawn reversely through saidexhaust port when the pump inlet is left connected to an evacuatedsystem.

3. In a vacuum pump a combination comprising a frame, a pump unit insaid frame having an inlet port and an exhaust port, a check valvecovering said exhaust port,

. said check valve including a fiat leaf spring secured at one end andcovering said exhaust port, means providing an oil bath for submergingsaid spring at a shallow depth under oil during the operation thereof,said leaf spring being slightly spaced away from said exhaust port whenthe leaf spring is in its unstresssed condition so that oil is suckedreversely through said check valve during a portion of each pumpingcycle of the pump unit, and means surrounding said spring for dammingand thereby limiting the flow of oil drawn reversely through saidexhaust port when the pump inlet is left connected to an evacuatedsystem, the frame of the pump being hollowed out adjacent the inlet portfor accommodating the oil drawn through said exhaust port.

4. In a vacuum pump the combination comprising a frame providing aninlet port, a pumping unit in said frame, said pumping unit having anexhaust port surrounded by a land portion and said pumping unit being soconstructed and arranged that a finite amount of air drawn through theinlet port is trapped and compressed into a small volume for dischargeat the exhaust port, a pair of flat elongated leaf springs arranged oneabove the other with one of the ends of the springs being anchored tosaid pumping unit and the other being positioned to overlie said exhaustport, the lowermost spring being so mounted that when the same is in itsunstressed condi tion the end of the spring is spaced a small amountabove the land surrounding said exhaust port and said lowermost springhaving an opening therein corresponding to the shape of the exhaustport, said upper spring having a sealing disc thereon and so mountedthat the disc bears without pressure against the lowermost spring whenthe upper spring is in an unstressed state.

References Cited in the file of this patent UNITED STATES PATENTS157,791 Cameron Dec. 15, 1874 919,036 Langer Apr. 20, 1909 1,768,844Holdsworth July 1, 1930 1,949,710 Dub-rovin Mar. 6, 1934 2,106,236 BurkeJan. 25, 1938 2,247,520 Paxton July 1, 1941 2,439,258 Matricon Apr. 6,1948 2,918,210 Touborg Dec. 22, 1959

1. IN A VACUUM PUMP A COMBINATION COMPRISING A FRAME, A PUMP UNIT INSAID FRAME HAVING AN INLET PORT AND AN EXHAUST PORT SURROUNDED BY A LANDPORTION, A CHECK VALVE COVERING SAID EXHAUST PORT, SAID CHECK VALVEINCLUDING AN UPPER LEAF SPRING AND A LOWER LEAF SPRING ARRANGED FLATLYFACE-TO-FACE, SAID LOWER LEAF SPRING BEING SLIGHTLY SPACED AWAY FROM THELAND SURROUNDING SAID PORT WHEN THE LEAF SPRINGS ARE IN THEIR UNSTRESSEDCONDITION, AND SAID LOWER SPRING HAVING AN OPENING THEREIN CENTERED WITHRESPECT TO SAID EXHAUST PORT, A CUSHIONING AND SEALING MEMBER INTERPOSEDBETWEEN SAID SPRINGS FOR SEALING THE OPENING IN THE LOWER SPRING WHEN AVACUUM IS DRAWN IN THE INLET